MCU chips include both digital and analog circuitry thereon for performing the various processes and functionalities available from the chip. In order to save power on MCU chips it is often necessary to enable a standby mode of operation wherein certain functionalities of the MCU chip are powered down or inoperative in order to conserve battery power. This enables the prolonging of battery life in state of the art, battery-powered, portable applications. An MCU chip having an on-chip power supply for digital circuits needs to be able to operate with low static (quiescent) power consumption while enabling the use of widely variable external supply voltages such as a battery for the chip. In order to save power when the MCU chip is not in use, a standby low power mode may be used to minimize power losses of the digital circuit when clocked by the system clock and to eliminate the quiescent current of the regulator and bandgap reference circuits. In some situations, the clock circuitry is halted, thus reducing power due to switching of digital circuitry. In other power saving applications, the complete chip is powered down and configuration information saved in non-volatile RAM (NVRAM). However, in this latter situation the MCU chip may be interfacing with other outside chips in an application system wherein these interfaces enable and disable the outside chips via control signals from the I/O ports of the MCU chip, such that there is no contention of states of the pins of the MCU and other peripheral devices connected to it.